This invention relates to a device for detecting a partial discharge taking place in electrical members to which a high voltage is applied, such as coils and connecting conductors, and more particularly to such a partial discharge detecting device for electrical equipments wherein an antenna is employed for detecting the partial discharge.
In transformers charged with a sulfur hexafluoride (SF.sub.6) gas, for example, organic high polymers such as polyethylene telephtalate are sometimes employed as a material of member for insulating coils. However, such organic high polymers as polyethylene telephtalate are inferior against an electric discharge. Since there is a possibility of reduction of the insulation capacity of the insulating member upon occurrence of a partial discharge in the coil, a sufficient consideration is given to the transformer in its designing stage for prevention of occurrence of the partial discharge in the coil as much as possible.
However, it is desirable that when a long period use causes the partial discharge in the coil of the transformer, the partial discharge is coped with as soon as possible. As a result, various methods of and devices for detecting the partial discharge in the transformers have been presented. Japanese Laid-open Patent Application (Kokai) No. 57-80572 discloses a method of detecting the partial discharge based on both current pulses and sound produced with the partial discharge. Another Japanese Laid-open Patent Application (Kokai) No. 57-112232 discloses a method of detecting a corona discharge by detecting electromagnetic waves discharged with the corona discharge by way of a loop antenna.
In accordance with the above-mentioned conventional methods, the detection signal is at a low level and the noise level thereof is relatively high. Consequently, a circuit is needed for removing the noise from the detection signal, which complicates the over-all arrangement of the partial discharge detecting device.